Tobacco smoke filter



United States Patent [72] Inventors Richard M. Berger Richmond;

Elwin W. Brooks, Mechanicsville, Virginia [211 Appl.No. 727,477

[221 Filed May 8, 1968 45] Patented Oct. 13, 1970 Assignee American Filtrona Corporation Richmond, Virginia a corporation of New York [5-1] TOBACCO SMOKE FILTER 30 Claims, 23 Drawing Figs.

[52] U.S.Cl 131/266. 131/105,l3l/l0.9,l3l/2l0 [51] lnt.Cl ..A24d01/04, A24d0l/l6 [50] FieldofSearch l3l/l0.

10.5.261-265tCursory) [56] References Cited UNITED STATES PATENTS 2 126.422 8/l938 Tarrant l3l/26lUX Primary Examiner-Melvin D. Rein Attorney-Jacobi, Davidson and Kleeman ABSTRACT: Filter elements, particularly for use with cigarettes and the like having relatively high filtration efficiency while otherwise satisfying ordinary commercial standards especially with respect to "taste", pressure drop and manufacturing cost. The filter means is constructed to provide a pair of elongated, high surface area, cavities defined on opposite sides of a relatively thin wall formed of filtering material. preferably only the ends of the filter means contacting an overwrapped outer tube thereby presenting maximum available surface area of the material from which the products are formed to the smoke for filtration. Filtration efficiencies (TPM) as great as in excess of 90 percent are shown with filter elements having commercially acceptable pressure drop and other such characteristics.

Patented Oct. 13,. 1970 Sheet I, SA

fia. 5%

e 5 MM w #3 w M vA770/(A/5V5' Patented Oct. 13; 1970 Sheet 3 01's TOBACCO SMOKE FILTER This invention relates to the production of filter means and relates more particularly to tobacco smoke filter elements. More specifically, the instant inventive concepts are primarily concerned with providing filter means for cigarettes, although the products of the instant invention are generally useful as fil ters, particularly for tobacco smoking means whether they be cigarettes, cigars, pipes or the like. Since filters for cigarettes are particularly commercially important, the basic embodiments of the instant invention will be discussed as they relate to the production of filtered cigarettes.

Various prior art techniques are known for making filters for use in connection with cigarettes and the like, although the resulting products, in general, have one or more disadvantages. Perhaps the most important property of a filter means is its efficiency, that is, its ability to remove undesirable constituents from tobacco smoke. Filtration efficiency is ordinarily measured in terms ofthe percentage of total particulate matter (TPM) removed from the smoke although there is also some concern for the percentage of gas phase constituents which a filter means is capable of removing, While filtration efficiency is perhaps the most important property of a cigarette filter means, it has been necessary, with prior art filter devices, to compromise the filtration efficiency in order to provide the filter with other properties such as pressure drop, taste, hardness, appearance and cost which are important from the standpoint of acceptability. For example, the most commonly utilized cellulose acetate filter means has a relatively low filtration efficiency since increased efficiency can only be obtained either by increasing the density of the filtering material or the length of the filter element, both of which produce a pressure drop across the filter which is excessive and unacceptable from a commercial standpoint While various suggestions have been made for the production of filter means which have improved filtering properties. such prior art developments have not become commercial either because the resultant filter means have been found to have objectionable taste characteristics whereby cigarettes providing with such filtering means fail to satisfy a large segment of the smoking public or because the techniques and/or the materials utilized in the production of such filter means have increased the costs excessively.

In any event, it is well known in the industry that there is no filter means presently on the market which provides relatively high filtration efficiency, on the order of60-95 percent (TPM), without suffering from undesirably high manufacturing costs, poor taste, high pressure drop or other such commercially unacceptable characteristics. The need and desirability of providing such a filter means is believed to be readily apparent, and the basic objectives of the instant inventive concepts are directed to this need. Consistent with the foregoing, this invention provides a filter means for use with a cigarette or the like having exceptionally high filtration effciency, in many embodiments removing as much as 95 percent of the total particulate matter, while having an acceptable pressure drop, as well as satisfactory taste, hardness and appearance. Further, and equally as important, this invention provides various techniques for the production of a filter means of the type described utilizing inexpensive materials in relatively small quantities as well as simple and efficient procedures whereby such filter means can be manufactured on a mass production basis at a cost which is at least comparable to the cost of production of presently utilized filter means. It should be realized that the ability to produce filter means for cigarettes and the like at minimal cost is critical to commercial acceptability of such products, and this invention provides processing techniques which permit high speed, continuous production of integral products of this nature without the need for handling special baffles or other extraneous elements which tend to slow down production rates and increase rejects clue to the difficulty in manipulating such small articles in a commercial operation.

Another feature of the instant invention is the provision ofa filter means which, in addition to having exceptionally high total particulate matter filtration efficiency, can be readily modified to provide exceptionally high gas phase filtration efficiency without adversely affecting the pressure drop,

taste hardness, appearance or cost. In this regard, a filter means can be produced according to the instant inventive concepts which includes a sorbent filtering material in particulate form having excellent gas or vapor phase filtration characteristics, such as, for example, activated carbon or the like while requiring a substantially smaller quantity of such particulate sorbent filtering material than prior art filter means which have included the same. with similar or better gas phase filtration efficiency. Further, this invention provides for the use of a filtration medium which can be tailormade" to fit the desired use with filtration efficiency, *taste properties and other such characteristics being readily modified by varying the materials utilized in the production of the filtration medium according to simple and inexpensive procedures.

Since, as the filter means of the instant invention is increased in length, the pressure drop across the same is decreased, the length of filter elements according hereto may be greatly varied and the density of the filtering medium may be greatly increased and additional filtering material may be incorporated therein without exceeding commercially acceptable pressure drop limits. Thus, a large variety of filtering materials may be utilized in accordance with the instant invention either alone or in various combinations to provide the final product with any desired characteristics.

Yet another feature of the instant inventive concepts is the provision of a filter means which, due to its unique construction and manufacturing methods, permits the same to be selfsustaining and self-centering, with an integral construction, and with a maximum available surface area being presented for filtration of smoke passing therethrough.

While the various disadvantages of prior art filter means and the techniques for making the same described hereinabove are believed to be representative of presently known products and manufacturing methods, it is to be understood that the foregoing is not intended to be comprehensive and, by contrasting the instant inventive concepts with the prior art, other undesirable features inherent in the latter will be readily recognized. Additionally, objects hereof other than those set forth previously will either be set forth specifically hereinafter or will be obvious from the following detailed description.

Such description makes reference to the annexed drawings wherein:

FIG. 1 is an enlarged fragmentary perspective view of a portion of a filtered cigarette incorporating a filter element according to one embodiment of the instant inventive concepts, parts being broken away and in section for illustrative clarity, and modifications of this embodiment of a filter means according hereto being shown in dotted line;

FIG. 2 is a schematic view of one embodiment of a method and means for making filter elements ofthe type shown for example, in FIG. 1;

FIGS. 2A2F are schematic views showing the individual steps and products resulting from the techniques of FIG. 2;

FIG. 3 is a transverse cross-sectional view taken substantially along lines 3-3 of FIG. 28;

FIG. 3A is a view similar to FIG. 3, but showing the use of a different form of filtering medium;

FIG. 3B is a view similar to FIG. 3, but showing the use of yet another form of filtering medium;

FIG. 4 is a transverse cross-sectional view taken substantially along lines 4-4 of FIG. 2C;

FIG. 4A is a view similar to FIG. 4, but showing the inner element crimped to a different configuration;

FIG. 4B is a view similar to FIG. 4, but showing the inner element crimped to yet another configuration;

FIG. 5 is a transverse cross-sectional view taken substantially on lines 5-5 of FIG. 2D;

FIG. 5A is a fragmentary cross-sectional view taken sub stantially along lines 5A-5A of FIG. 5;

FIG. 6 is a schematic view similar to FIG. 2 of portions of a method and means for forming filter elements similar to the type shown, for example, in FIG. 1. in a modified manner;

FIGS. 6A and 6B are schematic views showing two ofthe individual steps and products resulting from the techniques of FIG. 6;

FIG. 7 is a schematic view ofa still further modified method and means for forming filter elements similar to the type shown. for example, in FIG. I;

FIGS. 7A and 7B are schematic views of two of the individual steps and products resulting from the techniques of FIG. 7; and

FIG. 8 is a perspective view of a further embodiment of a filter element within the broad concepts of the instant invention.

Like reference characters refer to like parts throughout the several views of the drawings.

Referring now to the drawings in general. and more particularly to FIG. I, a portion of a filtered cigarette is designated generally by the reference numeral and comprises basically a tobacco portion 22 and a filter portion 24. The tobacco portion 22 comprises a rod of tobacco 26 overwrapped with paper or the like 28, as usual. The filter portion 24, in the embodiment shown in FIG. 1, comprises one form of filter element according to the instant inventive concepts designated generally by the reference numeral 30 and secured in end-toend relationship with one end of the tobacco portion 22 as by a tipping overwrap 32.

The filter element 30 includes basically an axially elongated, hollow, outer member 34 and an axially elongated, hollow, inner member, 36, disposed within the outer member 34.

In the embodiment of FIG. I, the outer member 34 is shown as a cylinder of ordinary plug" wrap as is conventionally used in the manufacture of filter elements for cigarettes. although this member may be formed of plastic or other materials, if desired.

The inner member 36 comprises what may be called a tube" formed primarily of any one or a combination of various filtering media as will be explained in more detail hereinafter. One end portion 38 is cylindrical providing peripheral portions of the outer surface of the inner member 36. limited in axial extent, which are juxtaposed to portions of the inner surface of the outer member 34 to at least substantially preclude axial passage of smoke across the area therebetween. Any desired adhesive means (not shown) may be included in this area to provide a smoke-tight seal, although the outer member 34 may merely be overwrapped about the inner member 36 to provide a substantially smoke-tight seal in this area. The important characteristic of this area is that smoke will pass through portions of the filtering material of the inner member 36 as explained hereinafter before bypassing the inner member across this area.

It will be noted that the major portions of the outer surface of the inner member 36 are spaced from the inner surface of the outer member 34 to define first elongated, high surface area. cavity means 40 therebetween, this cavity means including the area surrounding the end of the inner member 36 spaced from the sealed area at 38 particularly if this end of the inner member is spaced inwardly (not shown) from the corresponding end of the outer member 34.

First integral portions 42 of the inner member 36 define a first area which extends across the interior of the inner member 36 and which offers at least as much resistance to passage of smoke as the filtering material from which the inner member 36 is primarily formed. These first portions 42, in the embodiment of FIG. I, are defined by the end of the inner member 36 remote from the sealed area at 38 being crimped and preferably sealed, in a manner to be described in more detail hereinafter. In this manner, the use of a separate baffle or closing element is avoided. Basically, these first portions 42 preclude preferred entry of the smoke from the tobacco portion 22 into the interior of the inner member 36 through this end of the inner member 36 and insure that the smoke will pass more uniformly through the filtering material of the inner member 36 from the first cavity means 40. As will be seen in FIG. 1. the first portions 42 are crimped to form a generally or "Z"-shaped cross section. the laterally terminal edges 44 of which contact the inner surface of the outer member 34 to assist in centering the inner member 36 within the outer member 34 and in defining the first cavity means 40. In the preferred embodiment of this invention, only these laterally terminal edges 44 and the aforementioned peripheral portions 38 of the inner member 36 contact the outer member 34.'the remainder of the outer surface of the inner member 36 being spaced from the inner surface of the outer member 34 as will. be seen particularly in FIG. 5A. thereby utilizing the maximum available surface area for filtration.

Second portions 46 of the inner member 36 define a second area extending across the interior of the inner member 36 which offers less resistance to passage of smoke than the sealed area at 38. These second portions 46 may merely be the inner surface of the end portion of the inner member 36 remote from the first portions 42 which define an opening as shown in the full-line embodiment of FIG. 1. The interior of the inner member 36 between the first portions 42 and the second portions 46 defines second elongated, high surface area, cavity means 48. Thus, it will be seen that smoke passing through the filter element between opposite ends thereof must travel through both the first cavity means and the second cavity means 48 and must pass through the filtering material from which the inner member 36 is primarily formed. This construction provides an extremely high surface area for contact between the filtering material and the smoke, on the order of 7 times or more the surface area presented by the end portion of a conventional cellulose acetate filter. Yet, the construction of the instant invention, as will be readily recognized, and as will be seen from the comparative-data set forth hereinafter, provides substantially less pressure drop than a conventional cellulose acetate filter means of the same length. In this manner. extremely high filtration efficiency, once again as will be seen from the comparative data set forth hereinafter, will be provided by the filter means of this invention without encountering any difficulty with respect to pressure drop.

Since the pressure drop of a filter means according to the instant inventive concepts is quite low, it is possible to secure a plug or disk 50 of cellulose acetate or any other desired material within the open end of the inner member 36 as shown in dotted lines in FIG. I. This disk 50 then serves as the aforementioned second portions" of the inner member 36 and may be included, if desired, to merely provide the filter element 30 with the appearance of a solid plug. Further, the disk 50 may be utilized to increase the pressure drop of the filter means 30 to a desired level, depending upon .the characteristics of the material from which the disk is formed. Moreover, the disk 50 may be formed ofa material which provides the filter means 30 with particular taste" characteristics or which functions to enhance the filtering characteristics of the filtering material from which the inner member 36 is primarily formed by filtering out-certain constituents of the smoke which would otherwise pass through the filter means 30. Finally, the disk 50 serves to provide a second cavity means 48 having both ends closed whereby an additional smoke-modifying material 52 may be retained in the second cavity means 48. For example, this additional smoke-modifying material 52 may be a quantity of loose sorbent material in particulate form such as activated carbon or the like which enhances the vapor phase filtration efficiency ofa filter means according to the instant inventive concepts. It should be understood that this disk 50 is not necessary to the instant inventive concepts, and in fact, is ordinarily not utilized since it necessitates handling an additional element. However, for special effects, it may be included, if desired.

Reference is now made particularly to FIGS. 25 wherein a method and means for forming filter elements of the type shown in FIG. 1 is schematically designated by the reference numeral 60. A roll of filtering material in sheet form is provided at 62 and is passed through a means 64 wherein it is rolled in a well-known manner with the help of an endless belt 66 into an elongated, hollow, cylindrical inner element 68. The lateral edges 70 of the filtering material 62 may be provided with an overwrapped longitudinal seam according to conventional techniques, or a longitudinal butt seam as shown at 72 may be provided by application to the lateral edges of a hot melt plastic material from a dispenser such as shown at 74.

Prior to rolling the sheet 62 of filtering material into the inner element 68, stripes 76 of a hot melt plastic material may be applied to spaced locations on one side of the same by a dispenser such as shown at 78. For convenience purposes, these stripes 76 may be spaced apart a distance which is twice the length of a single filter element which is to be produced from the filtering material 62. For example, in the manufacture of 25 mm. filter plugs. the stripes 76 will be spaced apart by 50 mm. It will be seen that the inner element 68 has the stripes 76 of the hot melt plastic material disposed on the interior thereof.

Means 80 are then provided to crimp the inner element 68 at the aforementioned spaced location to provide alternating crimped portions 82 and uncrimped portions 84. The crimping means 80 may take any conventional form as may the other individual pieces of equipment described herein for use in the manufacture of filter means according to the instant invention. Further, although a hot melt plastic material is preferably utilized as the bonding means for the crimped portions 82, other bonding material may be utilized in place thereof. For example, stripes of a heat-activated. 041., thermoplastic, bonding material may be utilized and the crimping means 80 may be heated to activate the same.

The crimped inner element 86 is then overwrapped, for example, with a sheet of ordinary plug wrap such as shown at 88, by passing the crimped inner element 86 and the plug wrap 88 through a means 90 similar to the means 64, with the assistance of an endless belt 92 similar to the endless belt 66. The plug wrap 88 forms an axially elongated hollow outer element 94, the lateral edges of which may be secured together to form a longitudinal butt seam in the manner described hereinbefore with respect to seam 72 on inner element 68, or a longitudinal lapped seam as is well known, a heat sealing means 96 being shown for this latter purpose.

The overwrapped combined inner and outer elements 98 may then be cut in any conventional manner as by means schematically shown at 100 to provide a plurality of segments 102. For convenience in handling, each segment 102 may initially include four filter elements as shown in FIG. 2E, the segments being first further subdivided as shown by the dotted lines 104 to provide segments 106 each including two filter elements. The segments 106 may then be associated with a pair of tobacco portions 108 and overwrapped with a tipping paper 110 as shown in FIG. 2F before further subdividing the same as shown by the dotted line 112 to form two filtered cigarettes each including a single filter element of the type shown, for example, in FIG. 1.

The inner member may be formed of various different filtering materials, alone or in combination with each other. For example, the filtering material 62 may be ordinary filter paper or may be a sheet formed of various fibrous materials, either in staple or continuous filamentary form including ordinary plasticized or unplasticized secondary cellulose acetate. Additionally, the filtering material may consist of only paper pulp or a combination of blends of natural and man made fibers such as, for example, polyethylene, polypropylene, nylon, viscose, cellulose triacetate, glass fibers, asbestos fibers and the like. It has been found that for use as a cigarette filter, a blend of pulp formed of cotton linters or the like and secondary cellulose acetate is preferred for filtration. taste and cost considerations. Although cotton Iinter fiber pulp is indicated as desirable, any other conventional pulp material may be used such as kraft pulp fibers, sulphite pulp fibers, alpha pulp fibers, shredded bagasse fibers and mixtures thereof. Plasticized cellulose acetate may be used to bond the pulp, if

required. In particular, 25 percent or more secondary cellulose acetate, unplasticized or plasticized with glycerin triacetate or triethylene glycol diacetate will give, when blended with pulp, a filter which provides predominantly an acetate taste which is very desirable from a commercial standpoint.

The sheet material 62 may also have particulate sorbent filtering material such as activated carbon or the like or taste modifiers such as menthol or the like incorporated therein to provide the same with special characteristics. Additionally, if desired, particulate sorbent filtering material such as activated carbon or the like may be carried on one surface of the sheet 62 as shown at 114 in FIG. 3A thereby providing, in effect, a dual" layer of filtering material. Alternatively, a layer of such particulate filtering material I16 may be carried between a pair of layers of filtering material in sheet form 62', 62" as shown in FIG. 3B. In this manner, a laminated filtering material may be utilized for the manufacture of the inner member of the filter element. Although activated carbon has been. mentioned as the preferred particulate material, other well-known sorbent materials such as activated alumina, silica gel, molecular sieves and the like may be readily substituted therefor. Further, the filtering material may merely be formed of two or more layers in sheet form to provide a laminated arrangement. In addition to providing special characteristics such as good vapor phase filtration efficiency, ithas been found, as will be seen from the comparative datato be set forth in more detail hereinafter, that a plural layer filtering material formed into a filter means according to the instant inventive concepts, provides a combination screen-depth filter having particularly improved characteristics. For example, activated carbon used in the manner shown in FIG. 3A is found to have better vapor phase filtration efficiency than when such material is utilized in a bonded" filter means since the construction of the instant invention provides increased contact time thereby increasing the effectiveness of a given quantity of activated carbon.

The high surface area-low pressure drop characteristics of the filter means of this invention allows a wide choice 'in selecting filtering materials, sheet thickness, sheet density and filter length, such versatility being foreign to prior art filter constructions.

Although, in the embodiment of a filter means according. to this invention shown in FIGS. 1 and 4, the crimped portions 82 of the inner element 68 have been shown as 5" Z"-shaped in configuration, other configurations may be readily utilized. For example, in FIG. 4A, the crimped portions 820 are generally "Y"-shaped and in FIG. 4B. the crimped portions 8212 are shown as generally cruciformshaped. In any event. the laterally terminal edges of the crimped portions preferably contact the inner surface of the outer member. to assist in centering the inner member within the outer member and in defining the first cavity means in the manner shown, for example, in the embodiment of FIG. I.

Reference is now made particularly to FIGS. 6, 6A and 6 wherein portions of a modified technique for forming filter elements according to the instant inventive concept are schematically shown and designated generally by the reference numeral I20. Portions of this embodiment similar to the previous embodiment have been designated by the same reference numeral followed by an In this embodiment in addition to the use of a sheet of filtering material 62a a sheet of a porous thermoplastic material such as porous polyethylene or the like is provided as shown at 122. The porous thermoplastic material 122 replaces the stripes of bonding material 76 and provides the interior of the inner element 68a with a bonding means which can be activated upon crimping to seal the first portions of the inner member of the final product.

The dual layer, filtering material-porous thermoplastic material can also be formed in the manner shown in FIGS. 7, 7A and 7B wherein parts similar to the earlier embodiments are designated by the same reference numeral followed by a In this embodiment a strip of porous thermoplastic material 122b is helically wound about a mandrel 124, with the lateral edges thereof preferably in abutting or overlapping relationship. A strip of filtering material 62b is helically wound over the helically wound strip of thermoplastic material 1221; with the abutting or overlapping edges thereof preferably axially offset with respect to the underlying abutting or overlapping edges of the strip of thermoplastic material 122b. In this manner, a cylindrical element of filtering material may be provided with a continuous interior layer of porous thermoplastic material to provide bonding means for subsequent crimping. A heat sealing means 126 may be utilized to form the helically wound strips into a continuous element and, if desired, this element 68b may be subdivided as by a cutting means 1001; prior to crimping the inner element in a crimping means 80!). Cutting is effected before crimping with this embodiment due to the helical winding in the formation of the inner element 68b, although in the prior embodiments, the inner element may be first subdivided an subsequently crimped, if desired. The crimped inner elements I26 may be described, it will be readily recognized that numerous other embodiments having the same functional characteristics can be readily produced. For example, reference is made to FIG. 8 for an additional embodiment of an inner member which, when overwrapped with an outer member will function in a manner quite similar to the previously described embodiments. In the embodiment of FIG. 8. parts similar to earlier embodiments have been designated by the same reference numeral followed by the suffix In this embodiment, the inner member 36p-has outwardly flared portions at one end thereof to provide the peripheral portions 38c for sealing to the inner surface of an outer member, the opposite end portions of the inner member 360 being crimped as by twisting to close the same.

The foregoing embodiments are merely presented to emphasize the great versatility in materials and manufacturing techniques which are useful in the production of filter means without departing from the instant inventive concepts. The various details in the different embodiments may be combined to provide even further embodiments. Moreover, an individual filter element according to any of the embodiments shown, when associated with a rod of tobacco in a filtered cigarette, may be disposed with either end portion in facing relationship to the tobacco, although it has been found to be desirable to dispose the closed end portion, that is, the end having first portions 42, closer to the tobacco than the end having second portions 4 6 Further, a plurality of filter elements according to the instant inventive concept may be utilized with a single tobacco portion, or a filter element according to this invention may be utilized in combination with other forms of filter elements, if desired. However, the high filtration efficiency of filter means in accordance with this invention and the great versatility of such filter means in being capable of including one or more layers of various filtering media, ordinarily avoids the necessary for the use of multiple filters in a single filtered cigarette.

It should also be understood that, although the illustrative embodiments shown in the drawings and described hereinabove have utilized a separate tipping overwrap for securing a filter element according to the instant invention to a rod of tobacco, such tipping overwrap may, in and of itself, form the outer member of the filter means according to this invention thereby avoiding the necessity for an additional overwrap for this purpose. Such an arrangement is particularly useful when the inner element is to be subdivided prior to overwrapping as in the embodiment of FIG. 7 since the continuity of the manufacturing operation is interrupted at this point in any event whereby no significant advantage is obtained by being able to overwrap elongated inner elements to facilitate handling as with other embodiments.

The following comparative data is set forth to further illustrate the advantages of filter means formed in accordance with the instant inventive concepts. In such data, "Myria" filter elements are well known to those with ordinary skill in the art as the most efficient, presently available filter means, and "acetate filter elements refer to the most commonly utilized form of cellulose acetate filters commercially available. Pressure drop is the pressure differential between the ends of the rod or filter when air flows through it in the axial direction at 17.5 cc./sec. A pressure drop range of22.5 inches of water is presently preferred for a 20 mm. filter tip, although up to 3 inches of'water is acceptable and some commercially utilized filter plugs have even higher pressure drops, but filtered cigarettes incorporating the same must provide means for diluting the smoke with air in order that they may be utilized.

The total particulate matter filtration efficiency or percent retention (TPM) was determined by attaching 65 mm. length cigarettes to a 25 mm. tip and smoking the same on an automatic smoking machine, according to the well-known standard Cambridge method, taking 35 ml. puffs for 2 seconds each minute until a butt length of 15 mm. of tobacco was reached. The percent retention shows the proportion of the total particulate matter including water in the smoke produced by the tobacco rod that was retained by the filter in each instance.

Table 1 shows the properties of typical filters of the prior art as compared with a filter of the type shown in FIG. I hereof formed of a prior art commercial filter paper with the prior art and invention filters being compared at different pressure drops.

From the above, it will be readily recognized that the filter of the instant invention, at the same pressure drop, provides substantially higher filtration efficiency, in each instance in excess of 60 percent, and in some instances above percent. Yet, such extremely high filtration efficiencies are provided with extremely low pressure drops, in each instance below 2 inches of water. Moreover, such desirable characteristics are provided in a filter means which can be formed as a selfsustaining, self-centering, integral element in a highly efficient and continuous manner.

Table 2 compares a filter made according to the instant inventive concepts having a layer of cotton linter pulp carrying a coating of activated carbon in the manner of FIG. 3A, with a plug ofthe same length formed of solid bond ed carbon in the manner shown in U.S. Pat. No. 3.2 l 7,7 l 5. The quantity of acrolein through the filter has been selected as illustrative of the vapor phase filtration efficiency of the filter element.

From Table 2, it will be seen that a filter according to the in' stant inventive concepts traps more acrolein than a"bonded" carbon filter while utilizing less than one half the weight of carbon. Such a construction has obvious commercial importance in providing more effective use of the activated carbon thereby reducing the cost of the filter element while in creasing its filtration efficiency.

One of the characteristics of a filter formed according to the instant inventive concepts, that is, its decrease in pressure drop with an increased length, will be seen from Table 3 wherein filtration efficiency and pressure drop characteristics are compared for filter tips of different lengths, different material being utilized in the two experiments shown to provide different characteristics.

Table 4 compares filter thickness to pressure drop and retention ratio, this table being based on an experiment utilizing a sheet formed of a blend of 50 percent pulp and 50 percent secondary cellulose acetate.

TABLE 4 Thickness, Percent Inch P.l)., Inch Retention Although the above tables have shown illustrative results using particular materials or embodiments of this invention, similar results can be anticipated using other materials or embodiments of the instant inventive concepts.

From the above comparative data, it is believed that those skilled in the art will recognize the important commercial aspects of the instant inventive concepts. Although the above data has been generally directed to a filter means of the type shown in FIG. l, filter means formed according to any ofthe other embodiments hereof will provide similar highly improved filtration efficiencies at relatively low pressure drops. The skilled artisan may readily select one or more filtering media blended or laminated as described hereinabove to provide particular filtration, pressure drop. taste," hardness, appearance, cost or other properties. In any event, so long as the basic concepts hereof are followed, a filter means may be produced capable of removing exceedingly high percentages of undesirable constituents from tobacco smoke while satisfying all of the other properties which are necessary to commercial utility, particularly good taste" and pressure drop characteristics and low manufacturing costs. Accordingly,

We claim:

1. A filter means including a filter element comprising:

a. an axially elongated, hollow, outer member;

b. an axially elongated, hollow, inner member disposed within said outer member;

c. said outer member including an inner surface and an outer surface and having spaced end portions;

d. said inner member comprising a filtering material and including an inner surface and an outer surface and having spaced end portions:

integral peripheral portions of said outer surface of said inner member being juxtaposed to portions of said inner surface of said outer member to at least substantially preclude axial passage of smoke across the area therebetween:

. the major portions of said outer surface of said inner member being spaced from said inner surface of said outer member to define first elongated cavity means therebetween:

g. integral first portions of said inner member defining a first area extending across the interior of said inner member which offers at least as much resistance to passage of smoke as said filtering material, said first portions being axially spaced from said peripheral portions;

h. second portions of said inner member defining a second area extending across the interior of said inner member which offers less resistance to passage of smoke than the area between said peripheral portions of said inner member and said inner surface of said outer member, said second portions being axially spaced from said first portions toward said peripheral portions; and

. the interior of said inner member between said first and second portions defining second elongated cavity means, whereby smoke passing through said filter element between opposite ends thereof must travel through both said cavity means and through said filtering material.

2. A cigarette comprising, in combination, a tobacco rod and a filter means secured in end-to-end relationship to one end ofsaid tobacco rod, said filter means including a filter element as defined in claim 1.

3. The cigarette of claim 2 wherein said filter means is disposed such that said first portions of said inner member are closer to said tobacco rod than said second portions.

4. The filter means ofclaim 1 wherein said filter element has a pressure drop no greater than about 2.5 inches of water and a total particulate matter filtration efficiency of at least about 60 percent.

5. The filter means of claim 4 wherein said filter element has a total particulate matter filtration efficiency of at least about percent.

6. The filter means of claim 1 wherein said filtering material comprises at least about 25 weight percent secondary cellulose acetate.

7. The filter means ofclaim 6 wherein said filtering material comprises a blend ofsecondary cellulose acetate and pulp.

8. The filter means of claim 1 wherein said filtering material comprises a tubular layer of fibrous filtering material in sheet form carrying a sorbent particulate filtering material.

9. The filter means of claim 8 wherein said sorbent particulate filtering material is activated carbon.

10. The filter means of claim 1 wherein said filtering material comprises a pair of tubular layers of fibrous filtering material in sheet form with a sorbent particulate filtering material therebetween.

11. The filter means of claim 10 wherein said sorbent particulate filtering material is activated carbon.

12. The filter means of claim 1 wherein said second area is defined by one of said end portions of said inner member being open.

13. The filter means of claim 1 wherein said second area is defined by a plug of material extending across one of said end portions of said inner member, said plug being formed of a material offering less resistance to passage of smoke than the area between said peripheral portions of said inner member and said inner surface of said outer member.

14. The filter means of claim 13 further including a quantity of a further smoke-modifying material carried in said second cavity means between said first portions and said plug.

15. The filter means of claim 14 wherein said further smoke-modifying material is a loose, sorbent, particulate filtering material.

16. The filter means of claim wherein said sorbent particulate filtering material is activated carbon.

17. The filter means of claim 1 wherein said first area is defined by integral portions of said inner member twisted together at one of said end portions of said inner member.

18. The filter means of claim 1 wherein said peripheral portions of said inner member are formed by integral flared portions of said inner member at one of said end portions of said inner member.

19. The filter means of claim 1 wherein said first area is defined by integral portions of said inner member crimped together at one ofsaid end portions of said inner member.

20. The filter means of claim 19 wherein said crimped portions are sealed together by a bonding means.

21. The filter means of claim 19 wherein spaced parts of the periphery of said crimped portions contact said inner surface of said outer member to assist in centering said inner member within said outer member and in defining said first cavity means.

22. The filter means of claim 21 wherein said spaced parts of the periphery of said crimped portions contact said inner surface of said outer member only at said one end portions of said inner member, the entire outer surface of said inner member being spaced from said inner surface of said outer member except at said spaced end portions.

23. The filter means of claim 1 wherein said inner member is tubular, the outer surface of one end portion of said inner member defining said peripheral portions, the other end portions of said inner member being crimped and sealed together to define said first area, spaced parts of the periphery of said crimped portions contacting said inner surface of said outer member to assist in centering said inner member within said outer member and in defining said first cavity means, the inner surface of said one end portion of said inner member being open to define said second area.

24. The filter means of claim 23 wherein said spaced parts of the periphery of said crimped portions contact said inner surface of said outer member only at said other end portions of said inner member, the entire outer, surface of said inner member being spaced from said inner surface of said outer member except at said spaced end portions.

25. The filter means of claim 24 wherein said other end portion of said inner member is crimped to form a generally S" shaped cross section, only the laterally terminal edges of the "S"-shaped portions and said peripheral portions of said outer surface of said inner member contacting said inner surface of said outer member.

26 The filter means of claim 24 wherein said other end portion of said inner member is crimped to form a generally cruciform-shaped cross section, only the laterally terminal edges of the cruciform-shaped portions and said peripheral portions of said outer surface of said inner member contacting said inner surface of said outer member.

27. The filter means of claim 24 wherein said other end portion of said inner member is crimped to form a generally shaped cross section, only the laterally terminal portions of Y"-shaped portions and said peripheral portions of said other surface of said inner member contacting said inner surface of said outer member.

28. The filter means of claim 24 wherein said inner member includes a tubular element comprising filtering material. said inner surface of said other end portion of said tubular element carrying a bonding means sealing said crimped portions of said inner member. I

29. The filter means of claim 24 wherein said inner surface of said inner member comprises a porous thermoplastic material and said outer surface of said inner member comprises filtering material, said thermoplastic material defining a bonding means sealing said crimped portions of said inner element.

30. The filter means of claim 29 wherein said inner surface of said inner member is formed of a helically wound strip of said thermoplastic material and said outer surface of said inner member is formed of a helically wound strip of said filtering material overlying said thermoplastic material, juxtaposed edges of said helically wound strip of said filtering material being axially offset with respect to underlying juxtaposed edges of said helically wound strip of said thermoplastic material. 

